Sealants are used in a wide variety in the manufacture of vehicles. In general, sealants are chemical compounds and are employed to seal gaps between mechanical parts of vehicles. Depending on the use and the vehicle, certain requirements to the sealants have to be met. In particular, in aerospace industry, sealants are used most often, due to the great pressure differences experienced between the interior of an airplane or parts of an airplane and the outer atmosphere, in particular when flying at higher speeds and an altitude. Thus, not only fuel tanks and pipelines, but also doors, windows, interior and other panels, parts of the wings and so on need to be sealed. The requirements of the aerospace industry to the sealants employed are particularly strict. Not only good sealant properties over a long time are desirable, but also a certain resistance towards chemical influence such as fuel or deicing fluids or even hydraulic fluids. Apart from that, it is always desirable that sealant compositions may be easily applied in manufacturing processes and need as few as possible application steps or additional steps such as application of heat for curing.
Presently, sealants employed in aerospace industry are based on polysulfide chemistry. Polysulfide-based sealants exhibit a broad range of properties advantageous for the intended use, such as high flexibility and resistance to deicing fluid. Apparently, due to these properties, there is at the present point no alternative for polysulfide-based sealants available for most aerospace applications. However, there are certain disadvantages reported in conjunction with polysulfide-based sealants, such as high shrinkage (which means that several layers of sealant have to be applied), curing strongly dependent on humidity and temperature (meaning a limited manufacturing cycle), complicate handling of mixing ratios, high density, and strong odour. Moreover, it has been reported that sealants based on polysulfides are not resistant to Hydraulic Fluids used in present-day aircrafts.
Accordingly, there exists a need for alternative materials useful as sealants, in particular for aerospace applications. For example, WO2009/038960 A2 describes somewhat flexible two-part compositions comprising a first part comprising one or more nitrile-butadiene rubber and long chain diamine and a second part comprising an epoxy resin and a silicone resin or a resin comprising epoxy and silicone resins. While these compositions are described to be useful as sealants or coatings for in particular wooden surfaces, it further appears that they do not fulfil the requirements for sealants for aerospace applications.
Without contesting the technical advantages associated with the sealant compositions known in the art for sealants, in particular in the aerospace industry, there is still a strong need for curable sealant composition for use in aerospace applications.
Other advantages of the curable sealant compositions and methods of the present disclosure will be apparent from the following description.